Apelin is the endogenous ligand for APJ (APLNR, angiotensin receptor like-1). The APJ receptor is a member of the rhodopsin-like G protein-coupled receptor (GPCR) family. The apelin/APJ system has been observed in many tissues such as heart, kidney, pancreas, lung and the central nervous system. This suggests diverse roles of the system in the physiology and pathology of mammals.
Apelin peptides are processed from a 77 residue pre-pro form into smaller bioactive fragments, mainly a 36 residue form (Apelin 42-77—also referred to as Apelin-36) and a smaller 13 residue polypeptide (Apelin 65-77—also referred to as Apelin-13) Hosoya et al., J. Biol. Chem. 275:21061-21067, 2000. Apelin peptides were previously determined to be endogenous ligands for the orphan APJ receptor, a member of the seven transmembrane G-protein-coupled receptor superfamily. Tatemoto et al., Biochem. Biophysi. Res. Commun. 251:471-476, 1998. One of the shorter more active isoforms identified, pyroglutamated apelin-13 ([PE65]Apelin-13 (65-77), has been reported to be the most potent and abundant form of apelin in cardiac tissue. Maguire et al., Hypertension 54:598-604, 2009. In vitro and preclinical models have suggested that the apelin/APJ system has a role in cardiovascular homeostasis as well as metabolism. Barnes et al., Heart 96:1011-1016, 2010. Circulating apelin levels are transient and Apelin-13 has a brief plasma half-life of <5 min leading to short-lived cardiovascular effects.
In vitro, exogenous apelin increases contractility at subnanomolar concentrations in atrial strips and whole rat hearts, and increases sarcomere shortening by up to 140% in isolated cardiomyocyctes. Barnes et al., Heart 96:1011-1016, 2010. Apelin also has a potent inotropic effect in an ex vivo isolated heart assay. In vivo, acute apelin infusion restores ejection fraction, increases cardiac output and reduces left ventricular end-diastolic pressure in rats with chronic heart failure. Berry et al., Circulation 110:187-193, 2004. Exogenous apelin potently enhances myocardial contractility without inducing left ventricular hypertrophy concomitant with reduction in ventricular preload and afterload. Barnes et al., Heart 96:1011-1016, 2010.
Studies from Kawamata et al and Hosoya et al have shown that that shorter peptide apelin-13 had approximately a 3.5-fold higher in vitro affinity to the APJ receptor than apelin-36. Kawamata et al., BBA 1538: 162-171, 2001, Hosoya et al., JBC 275: 21061-21067. Apelin-13 analogues were reported having a single substitution with either canonical or non-canonical amino acids. The authors also reported double and triple substitutions in apelin 66-77 and apelin 63-77, but not in apelin-13. The emphasis was on peptides reported to have higher in vitro affinity and potency than apelin-13. Nishizawa et al., in: T. Shioiri (ed.), Peptide Science 2000: Proceedings of the 37th Japanese Peptide Symposium, pp. 151-154. Several if not all of these modified peptides are reported in later studies. U.S. Pat. No. 7,635,751.
In a 2003 study (Medhurst et al., J. Neurochemistry 84:1162-1172, 2003) in vitro activity of apelin-36, apelin-17 and apelin-13 was compared. It was concluded that all three peptides were approximately equipotent. C-terminal amidation resulted in about a 14-fold decrease in affinity. A more recent study (Hamada et al., J. Mol. Med. 22:547-552, 2008) reported cyclic analogues of apelin-13. When tested for in vitro activity all three analogues maintained function activity, although with reduced potency relative to apelin-13.
A shortened 12 amino acid-apelin peptide having ligand activity on APJ was reported in a 2009 patent (U.S. Pat. No. 7,635,751). The peptide could have a substitution of one non-canonical amino acid. In another application, WO 2013/111110 A2 and U.S. Pat. No. 8,673,848, cyclic mimetics of apelin have also been reported.
Another study reported synthesizing analogs of apelin-13 with amino acid substitutions with non-canonical amino acids at the C-terminal end of the molecule but no pegylation at the N- or C-terminus or another site specific location. The use of internal PEG spacers (short PEG (n=4 or 6), however, was also reported in lower activity peptide analogs with deletions in the middle of the sequence that contained fewer amino acid residues than apelin-13. Murza et al. Chem Med Chem 7:318-325, 2012. Additionally, PCT/US2013/075773 describes a group of modifications, including substitution of non-canonical amino acids and changes at the N- and C-terminal of the apelin molecule that can affect, inter alfa, the potency of the molecule. The increased potency can be a result of increased half-life or decreased degradation relative to wild-type apelin.
Despite the advancements that have been made with respect to peptides, a need exists for small molecule agonists of the APJ receptor. However, some progress has been made in this area. For example, WO 2014/044738 discloses various benzimidazole-carboxylic acid amide derivatives as modulators of the APJ Receptor. Other small molecule agonists of the APJ receptor are disclosed in U.S. Pat. Appl. Pub. No. US 2016/0340336, WO 2016/187308, WO 2015/184011, and WO 2015/188073.
A need continues to exist for agonists of the APJ receptor that may be used to treat various cardiovascular and other conditions. The present application discloses such agonists of the APJ receptor s that may be suitable for use as therapeutic agents in treating a variety of conditions. These compounds may find particular benefit in treating cardiovascular conditions. For example, such compounds may be beneficial in treating conditions such as chronic systolic heart failure and chronic diastolic heart failure.